ANNUAL REPORT, 1946-47 37 



application, sabadilla gave very good control but appeared to have very little 

 residual value. Ryanex dust appeared to kill rather slowly but to furnish good 

 lasting effects. DDT dusted plants showed even fewer thrips after a 7-day 

 interval than 24 hours after the application. 



None of the sprays or dusts used caused any plant injury. 



Control of Squash Vine Borer. (W. D. Whitcomb, Waltham.) Experimental 

 plantings in 1946 verified previous observations that varieties of Cucurbita mos- 

 chata are immune to squash vine borer. Three varieties of C. maxima averaged 

 2.88 borers per vine, and three varieties of C. pepo averaged 1.70 borers per vine. 



Insecticide applications in Julj' with 3 percent DDT-talc dust, 20 percent 

 sabadilla-lime dust, and J^ percent DDT plus 0.06 pj'rethrins dust gave satis- 

 factory protection; while applications of 10 percent sabadilla-lime dust and 3^ 

 percent DDT-talc dust were unsatisfactory as used. 



A 5 percent benzine hexachloride-talc dust applied while the plants were small 

 caused so much injury that it was necessary to replant. The 3 percent DDT- 

 talc dust caused slight temporary stunting to seedlings, which was most evident 

 on cucumbers and least evident on Blue Hubbard squash. 



Control of Cabbage Maggot. (W. D. Whitcomb, Waltham.) Field treatments 

 for the control of the cabbage maggot in early Golden Acre cabbage were com- 

 pared with a natural 100 percent infestation on untreated plants, in which 84 

 percent of the plants were commercially damaged. DDT-talc dust, both 3 and 

 5 percent DDT, applied either with a hand duster in two applications at a weekly 

 interval, or placed in a mound around the stem of the plant soon after the first 

 eggs were laid, permitted 20 to 25 percent infestation and from 20 to 40 percent 

 of the heads were unmarketable. Corrosive sublimate solution 1-1,280 in two 

 applications, and 4 percent calomel-talc dust in*a mound around the stem gave 

 perfect protection from commercial injury. However, the outstanding treatment 

 was two applications with a hand duster of benzene hexachloride-talc dust con- 

 taining about 5 percent of the gamma isomer. This dust completely controlled 

 the maggot on both cabbage and cauliflower as well as preventing blind heads 

 due to cutworm injury. No evidence of contamination by the odor of the in- 

 secticide was evident at any time after Ih'e heads began to form. This treatment 

 promises to have great commercial application. 



Biology and Control of Red Spider Mite on Greenhouse Crops. (W. D. Whit- 

 comb, Wm. Garland, and C. S. Hood, Waltham.) Spraying of greenhouse roses 

 with hexa ethyl tetra phosphate solution resulted in excellent control of green- 

 house red spider, but caused some injury to foliage and stunted the growth of the 

 petals on the outside of rosebuds. Two commercial brands of this niaterial diluted 

 as recommended were equally effective and caused similar plant injury. 



The effect of sodium selenate in red spider control was studied on potted car- 

 nations at low temperatures (55° F.) during the winter. Dosages of J^ gram, 

 % gram, and 1 gram per square foot caused a reduction in the spider population 

 50 days after treatment, and remained effective for 50 days longer (100 daj's 

 after application). A dosage of H gram per square foot became noticeably 

 effective 60 days after application and remained effective only 30 daj's. Spider 

 populations were not reduced as much by the dosages used as they were by similar 

 treatments in spring and summer. 



